In recent years, technologies have been developed for utilizing a variety of energy resources from the viewpoint of the environmental measure, saving resources and saving energy. Among them is a technology for taking out the mechanical energy from the thermal energy present in the natural world, such as solar heat. Technologies have also been developed to improve the thermal efficiency of an internal combustion engine by recovering the power which is generated by utilizing the exhaust heat into the exhaust gas or into the cooling water of an internal combustion engine such as diesel engine, and the like.
Heat engines are used for converting the thermal energy into the mechanical energy such as rotational energy. The heat engines include internal combustion engines that use the air elevated to a high temperature and a high pressure by the combustion directly as the operation fluid and external combustion engines that produce the operation fluid of a high temperature and a high pressure by the conduction of heat. It is not allowed to use the internal combustion engine for converting the heat energy in the natural world or the thermal energy of the internal combustion engine into the mechanical energy. Therefore, the steam engine which is an external combustion engine is much used. Usually, the steam engine is equipped with a steam generator such as a boiler for generating the steam by using the heat of a heat source, an expansion machine such as a steam turbine for generating the power, a condenser for condensing the expanded steam and a condensate pump for refluxing the condensate into the steam generator. Therefore, the constitution is complex and is large in scale.
The internal combustion engine or the external combustion engine that uses an ordinary fuel such as petroleum, natural gas or the like, is the one in which the fuel is burned to produce an operation fluid of a high temperature and a high pressure and the thermal energy is converted into the mechanical energy, and features a high thermal efficiency since the mechanical energy is taken out from the heat source in the state of a high temperature. However, the thermal energy in the natural world and the exhaust heat of the internal combustion engine are, usually, the thermal energies which do not have so high temperature, i.e., which are in a low-temperature state. In order to efficiently take out the mechanical energy from such heat sources, therefore, it becomes necessary to use a heat engine adapted to the heat source in a low-temperature state.
The engine disclosed in JP-A-2001-20706 is a heat engine which is relatively simply constituted for generating the mechanical energy from the heat source in a low-temperature state. As shown in FIG. 6, this engine comprises a steam-generating portion 101 and a cooling portion 102 which are coupled together through nozzles 103. A turbine 106 is arranged in the cooling portion 102 at a position facing the nozzles 103, and rotates together with magnets 107. On the inside of the magnets 107, a stationary generating coil 110 is arranged facing thereto, and the magnets 107 and the generating coil 110 together constitute a generating device. The steam-generating portion 101 and the cooling portion 102 are sealed, respectively. Water 104 which is an operation fluid is filled therein, and the air inside is evacuated by a vacuum pump. Many heat pipes 105 for heat radiation are mounted on the upper side of the cooling portion 102.
The steam-generating portion 101 and the cooling portion 102 as a whole constitute a heat pipe, and water 104, which are heated up in the steam-generating portion 101 from the lower side thereof and become steam, create a high-speed stream which is jetted to the blades of the turbine 106 from the nozzles 103. Accordingly, the turbine 106 and the magnets 107 rotate to produce the rotational energy which is, finally, converted into the electric energy by the magnets 107 and the generating coil 110, and is output to an external unit. The steam after having driven the turbine 106 is cooled down with the heat-radiating action of the heat pipes 105 and returns back to water. The condensate falls down to the lower side of the cooling portion 102 due to gravity, and is refluxed into the steam-generating portion 101 through the central portion.
The heat pipe that utilizes vaporization and condensation of liquid contained in the sealed container is, usually, used as a heat conveying means, i.e., as a heat transfer device. Here, the steam of liquid contained in the heat pipe moves accompanying large velocity energy and, therefore, the power can be taken out therefrom as described above. In this case, the mechanical energy can be taken out from the heat source in a low-temperature state.
The turbine disclosed in the above JP-A-2001-20706 is a so-called velocity type engine which utilizes the velocity energy of the operation fluid. To efficiently operate the turbine, the rotational speed of the turbine must be increased so that the circumferential velocity thereof is increased to match the velocity of the steam. However, when decreasing the diameter of the turbine to miniaturize it, the rotational speed of the turbine becomes very high and a large centrifugal force acts on the turbine and may break it down. To drive the load by using an engine which revolves at high speeds, further, it becomes necessary to provide a reduction gear to lower the rotational speed. When it is attempted to take out the power in the form of electric energy by a generator, a peripheral control unit and the like being necessary for the high speed generator are complex and expensive.
In the turbine device as disclosed in the above publication, nozzles are arranged in the inlet of the turbine in an attempt to increase the velocity energy of the steam which is the operation fluid. Therefore, the distance becomes relatively long between the heating portion and the turbine, and the steam is cooled therebetween resulting in a loss of heat. Further, when the temperature of the heating portion is low and the steam is of a low temperature, the steam is superheated to only a low degree, and water droplets tend to form due to the cooling. Water droplets that are formed come into collision with the turbine blades at high speed, and the turbine blades develop the so-called erosion due to the collision with water droplets.
When the heat engine is rotated being contained in a closed container, the rotary shaft must be supported by bearings having sealing performance. To support the rotary shaft that rotates at high speed such as of the turbine, precision bearings are necessary. Namely, complex and expensive bearings must be used to support the rotary shaft maintaining sealing performance requiring an increased cost for the maintenance.
The assignment of the present invention is to provide a heat engine capable of obtaining the mechanical energy not only from the heat sources of high temperatures but also from various heat sources in a low-temperature state, such as exhaust heat of an internal combustion engine while solving the above-mentioned problems inherent in the conventional heat engines.